Natural optical activity and its control by electric field in electrotoroidic systems

Abstract

We propose the existence, via analytical derivations, novel phenomenologies, and first-principlesbased simulations, of a new class of materials that are not only spontaneously optically active, but also for which the sense of rotation can be switched by an electric field applied to themvia an induced transition between the dextrorotatory and laevorotatory forms. Such systems possess electric vortices that are coupled to a spontaneous electrical polarization. Furthermore, our atomistic simulations provide a deep microscopic insight into, and understanding of, this class of naturally optically active materials.

Axial hypertoroidal moment in a ferroelectric nanotorus: A way to switch local polarization

“…Thus, it may exhibit an optical activity that could possibly be tuned by modulating hypertoroidal moment and/or toroidal moment. Such a behavior has recently been simulated in the case of an array of aligned BaTiO 3 nanowires embedded in a SrTiO 3 matrix [25]: Well-separated nanotori embedded in a matrix could offer an alternative route for an experimental realization of such an optical modulator that would have the ability to change from levorotatory to dextrorotatory optical behavior.…”

Dynamical magnetoelectric effects associated with ferroelectric domain walls

“…On the other hand and as shown in Ref. [14], a non-zero macroscopic magnetization can be created by a non-zero time-derivative of the electrical toroidal moment (which is precisely the case for the studied domain structure under ac electric field and which is associated with inhomogeneous polarization field).…”

“…where M is the magnetization (in SI units) at time t, while M 0 is the part of magnetization that is not related to the change of polarization [14]. Figure 1a shows the macroscopic polarization P along the z axis as a function of time.…”

“…For that, we perform firstprinciples-based molecular dynamics simulations on Pb(Zr,Ti)O 3 (PZT) ultra thin films being under an ac electric field and possessing up and down nanoscale domains. Based on the recently discovered relationship between the time derivative of the electric toroidal moment and magnetization [14], it is indeed predicted that a magnetization should occur in these systems. This magnetization has two different features and microscopic origins: it can be due to the change of magnitude of electric dipoles within non-moving "up" and "down" domains, and can also exhibit pulses when domains move via sudden change of their morphology.…”

“…The time derivative of the electric toroidal moment is also computed since, according to Ref. [14], it is proportional to the dynamical change of the magnetization:…”